Flange focal distance
For an interchangeable lens camera, the flange focal distance (FFD) (also known as the flange-to-film distance, flange focal depth, flange back distance (FBD), flange focal length (FFL), or register, depending on the usage and source) of a lens mount system is the distance from the mounting flange (the metal ring on the camera and the rear of the lens) to the film plane. This value is different for different camera systems. The range of this distance which will render an image clearly in focus within all focal lengths is usually measured in hundredths of millimeters and is known as the depth of focus (not to be confused with the similarly named depth of field).
This distance influences whether a lens from one system can be mounted with an adaptor to a camera body of another system. In order to produce an adaptor that permits focus to infinity without corrective optics, the flange-to-film distance the lens is designed for must be greater than that of the camera body it is to be adapted to, giving room for the adaptor. Camera systems with a large flange-to-film distance have lenses that can be widely adapted, while those with a small flange-to-film distance can take adaptors for many types of lenses.
If the difference is small, other factors, such as the diameters of the mounting flanges of the two systems, come into play as well. Lens adapters are generally easier to make when the camera body has a large lens mount.
Standard mounts include:
Mount | Flange focal distance |
Type | Format | Production | Prime lenses | Zoom lenses | Wide/tele converters | Mount converters | Comments |
---|---|---|---|---|---|---|---|---|---|
Pentax Q-mount | 9.2 mm[1] | Mirrorless | 1/2.3" (6.17×4.55 mm) | 2011– | 4 | 2 | 0 | 0 | |
1/1.7" (7.44×5.58 mm) | 2013– | 1 | 1 | 0 | 1 | ||||
D-mount | 12.29 mm | cine | 8 mm | (8 mm movie cameras) | |||||
CS-mount | 12.50 mm[2] | TV | 1/4", 1/3", 1/2" | (surveillance cameras) | |||||
Nikon 1-mount | 17 mm[3] | Mirrorless | CX | 2011– | 1 | ||||
C-mount | 17.526 mm[2] | cine / TV | 8 mm, 16 mm, 1/3", 1/2", 2/3", 1", 4/3" | ~1926– | (Bolex, Eclair and Bell & Howell) | ||||
Fujifilm X-mount | 17.7 mm | Mirrorless | APS-C | 2012– | 8 | 8 | 0 | 1[4] | |
Canon EF-M-mount | 18 mm | Mirrorless | APS-C | 2012– | 1 | 3 | 0 | 1 | |
Sony E-mount | 18 mm | Mirrorless | 24×36 mm / APS-C | 2010– | 6 | 10 | 4 | 2 | |
24×36 mm (FE) | 2013– | 5 | 6 | 2 | 2 | ||||
Sony FZ-mount | 19 mm | cine | Super 35 mm | 2011– | 0 | 2 | 0 | 3 | |
Leica SL-mount (formerly T) | 19 mm | Mirrorless | 24×36 mm / APS-C | 2014– | 1 | 3 | |||
24×36 mm | 2015– | ||||||||
Micro Four Thirds System | 19.25 mm | Mirrorless | 17.3mm x 13mm/four thirds | 2008– | 22 | 17 | |||
Samsung NX-mount | 25.50 mm | Mirrorless | APS-C | 2010– | 5 | 4 | |||
Pentax Auto 110 | 27 mm | SLR | 13×17 mm | 1978–1985 | 5 | 1 | 0 | 0 | |
RED ONE interchangeable mount | 27.30 mm | cine | |||||||
Leica M-mount | 27.80 mm[4] | Mirrorless | 24×36 mm | 1954– | aka Voigtländer VM-mount, Epson EM-mount, Zeiss ZM-mount as well as Konica KM-mount (Hexar RF) and Minolta M-mount (CL/CLE) | ||||
M39×26tpi mount | 28.80 mm | Mirrorless | 24×36 mm | Leica M39×26tpi aka L39 (not to be confused with M39×1) | |||||
Contax G-mount | 29.00 mm | Mirrorless | 1994–2005 | 6 | 1 | 0 | 1 | ||
Olympus PEN F | 28.95 mm | SLR | 18 x 24 mm | 1963–1972 | 16 | 2 | |||
Contax RF-mount | 34.85 mm | Mirrorless | 24×36 mm | ||||||
Nikon S-mount | 34.85 mm | Mirrorless | 24×36 mm | 1947–2005 | |||||
1/2" TV bayonet mount | 35.74 mm | TV | 1/2" 3-CCD | JVC, Hitachi, Panasonic, others, but not Sony | |||||
Minolta V-mount | 36.00 mm | SLR | APS-H | 1996–1999 | 3 | 5 | 0 | 1 | Vectis S-1, Vectis S-100, Dimáge RD-3000 |
Sony 1/2" TV bayonet mount | 38 mm | TV | 1/2" 3-CCD | ||||||
Olympus Four Thirds System | 38.67 mm | SLR | 4/3" | 2003– | 12 | 30 | 2 | ||
Konica F-mount | 40.50 mm | SLR | 24×36 mm | 1960–1965 | 17 | 0 | 0 | 0 | |
Konica AR-mount | 40.50 mm | SLR | 24×36 mm | 1965–1988 | 36 | 16 | 1 | 0 | |
Canon FL-mount | 42.00 mm | SLR | 24×36 mm | 1964–1971 | |||||
Canon FD-mount | 42.00 mm | SLR | 24×36 mm | 1971–1990 | 107 | 34 | |||
Start (Soviet SLR) | 42.00 mm | SLR | 1958–1964 | ||||||
Minolta SR-mount | 43.50 mm | SLR | 24×36 mm | 1958–2001 | 6 | ||||
Fujica X-mount | 43.50 mm | SLR | 24×36 mm | ||||||
Pentaflex (16 mm cameras) | 44 mm | cine | |||||||
Canon EF-mount | 44.00 mm | SLR | 24×36 mm / APS-C | 1987– | 47 | 64 | |||
Canon EF-S-mount | 44.00 mm | SLR | APS-C | 2003– | 2 | 9 | 0 | 0 | |
Praktica B-mount | 44.00 mm | SLR | 24×36 mm | ||||||
Sigma SA-mount | 44.00 mm | SLR | 24×36 mm / APS-C | 1992– | 0 | ||||
Minolta/Konica Minolta/Sony A-mount | 44.50 mm | SLR | 24×36 mm | 1985– | 42+0+17 | 50+2+13 | 6+0+2 | 2+0+0 | |
APS-C | 2004– | 0+0+3 | 0+3+13 | 0+0+0 | 0+0+0 | ||||
QBM | 44.5 mm[5] | SLR | 24×36 mm | Rollei, Voigtländer | |||||
Exakta | 44.7 mm[6] | SLR | 24×36 mm | 1936–1969 | |||||
M39x1 | 45.2 mm[7] | SLR | 24×36 mm | 1952–1968 | Early Russian SLRs (Zenit) (not to be confused with M39×26tpi and M39×1/28,8) | ||||
M42×1 | 45.46 mm | SLR | 24×36 mm | 1949– | Pentacon, Pentax, Contax S, Praktica, Zeiss ZS, Zenit (not to be confused with M42×0.75) | ||||
Pentax K-mount | 45.46 mm | SLR / Mirrorless | 24×36 mm | 1975– | 131 | 77 | |||
Contax C/Y-mount | 45.50 mm | SLR | 24×36 mm | 1974–2005 | 24 | 5 | 3 | ||
Mamiya Z | 45.50 mm | SLR | 24×36 mm | 1980– | |||||
Kodak Retina DKL-mount | 45.7 mm | SLR / Mirrorless | 24×36 mm / 28×28 mm | 1958–1977 | 12+6 | 0 | 0 | 0 | DKL variants used by Retina Reflex S (034), Retina Reflex III (041), Retina Reflex IV (051, 051/N), Instamatic Reflex (062), Retina IIIS |
Voigtländer Bessamatic DKL-mount | 45.7 mm | SLR | 24×36 mm | 1958–1967 | 11+2 | 1 | 0 | 0 | DKL variants used by Bessamatic, Bessamatic deLuxe, Bessamatic m, Bessamatic CS, Ultramatic, Ultramatic CS |
Braun Paxette Reflex DKL-mount | 45.7 mm | SLR / Mirrorless | 24×36 mm | DKL variant used by Paxette Reflex Automatic, Paxette Reflex Automatic II, Tower 33 Reflex, Tower 34 Reflex; Balda Baldamatic III; Witt Iloca Electric / Graflex Graphic 35 Electric; Wirgin Edixa Electronica / Revue Edixa Electronica | |||||
Voigtländer Vitessa T DKL-mount | 45.7 mm | Mirrorless | 24×36 mm | 4+? | 0 | 0 | 0 | DKL variant used by Voigtländer Vitessa T; Braun Colorette (Super) II, Colorette (Super) IIB, Colorette (Super) IIL, Colorette (Super) IIBL; Wittnauer Continental, Wittnauer Professional | |
Yashica MA-mount | 45.8 mm | SLR | 24×36 mm | 1 | (measured); 230AF etc. | ||||
Olympus OM-mount | 46.00 mm | SLR | 24×36 mm | 1972–2002 | 38 | 14 | |||
Nikon F-mount | 46.50 mm | SLR | 24×36 mm / APS-C | 1959– | ? | ? | |||
Leica R-mount | 47.00 mm | SLR | 24×36 mm | 1964–2009 | |||||
KMZ Zenit DKL-mount | 47.58 mm | SLR | 24×36 mm | 1964–1968 | 5 | 1 | 0 | 0 | Zenit/Зенит 4/5/6 "Байонет Ц", an unofficial DKL-mount variant |
B4 2/3" TV bayonet mount[8] | 48.00 mm | TV | 2/3" 3-CCD | 1992– | Unofficially known as "B4 mount" | ||||
Contax N-mount | 48.00 mm | SLR | 24×36 mm | 2000–2005 | 4 | 5 | 0 | 1 | |
Arri STD | 52.00 mm | cine | |||||||
Arri B | 52.00 mm | cine | |||||||
Arri PL | 52.00 mm | cine | |||||||
Mini T-mount | 55.00 mm | SLR | 24×36 mm | 1957–1962 | Taisei, M37×0.75 | ||||
T-mount | 55.00 mm | SLR | 24×36 mm | 1962– | Tamron T-400, M42×0.75 (not to be confused with M42×1) | ||||
YS mount | 55.00 mm | SLR | 24×36 mm | –1969 | Sigma, Upsilon, Accura, Polaris, Sun, Aetna, Beroflex, Petri, Raynox, N.P.S., Formula, Dionar, Universal, Soligor, Yashica, Spiratone. M42×0.75 (not to be confused with M42×1) Same as T-mount but with aperture coupling | ||||
Panavision PV-mount | 57.15 mm | cine | 1972– | 35 mm & 16mm | |||||
OCT-19 | 61.00 mm | cine | |||||||
Mamiya 645 | 63.30 mm | SLR | 6×4.5 cm | ||||||
Novoflex A-mount | 63.3 mm | SLR | (measured) "A"-type adapters for follow-focus system | ||||||
Contax 645 | 64.00 mm | SLR | 6×4.5 cm | ||||||
Pentax 645 | 70.87 mm | SLR | 6×4.5 cm | 1984– | |||||
Rollei SLX | 74.00 mm | SLR | 6×6 cm | –2005 | |||||
Pentacon Six | 74.1 mm | SLR | 6×6 cm | 1956–1992 | |||||
Hasselblad 2000 & 500 | 74.90 mm | SLR | |||||||
Hasselblad 1000F & 1600F | 82.10 mm | SLR | |||||||
Pentax 6×7 | 84.95 mm or 85.00 mm | SLR | 6×7 cm | 1969–1999 | |||||
Rollei SL66 | 102.80 mm | SLR | 6×6 cm | ||||||
Mamiya RZ67 | 105 mm | SLR | 6×7 cm | ||||||
Mamiya RB67 | 111 mm | SLR | 6×7 cm |
Flange focal distance is one of the most important variables in a system camera, as lens seating errors of as little as 0.01 mm will manifest themselves critically on the imaging plane and focus will not match the lens marks. Professional movie cameras are rigorously tested by rental houses regularly to ensure the distance is properly calibrated. The most common mount is the Arri PL mount with an FFD of 52.00 mm. The Russian OCT-19 has an FFD of 61.00 mm. C-mount (Bolex, éclair and Bell & Howell) has 17.52 mm. Any discrepancies between eye focus and measured focus which manifest themselves across a range of distances within a single lens may be collimation error with the lens, but if such discrepancies occur across several lenses, it is more likely to be the flange focal distance or the groundglass (or both) which are mis-set.
Due to research on optimal flange focal distance settings, it is currently considered better for flange focal distance to be set to somewhere within the film's emulsion layer, rather than on the surface of it. Therefore, the nominal flange focal depth will be equivalent to the distance to the groundglass, whereas the actual flange focal depth to the aperture plate will in fact be ~0.02 mm less.
See also
References
- Markerink, Willem-Jan. Camera Mounts & Registers. Retrieved on November 6, 2005.